A study published in Nature Communications found that water from hospital sewers promoted the growth of antibiotic-resistant bacteria. CIDRAP has the news.

The water from municipal treatment plants that the researchers looked at had no effect in comparison. The senior study author wrote that this provides direct evidence linking antibiotics excreted by hospital patients to observed environmental effects and highlight hospital sewers as a more likely site for resistance evolution than previously considered.

In Sweden, where the research was conducted, more than one in three hospital patients are receiving antibiotics at any given time. The study sought to answer whether the presence of antibiotic residues and resistant bacteria from patients creates selection pressure for the emergence of resistant bacteria in hospital sewers.

The researchers collected samples from hospitals and treatment plants and then exposed E coli isolates to them. Then, they placed plastic plates in the sewer pipes of the hospital and municipal sites for 30 days, then analyzed the biofilms that grew. There was significantly higher resistance to ciprofloxacin and cefotaxime in the hospital biofilms compared with the hospital wastewater, which the authors say provides direct evidence of resistance selection occurring naturally in the hospital sewer environment.